You have to make sure that the water supply tube (the one with the adjustment screw) is positioned at an angle into the corner of the cistern,with the adjustment screw facing towards the front of the cistern, exactly as shown in the assembly instruction leaflet. otherwise the float tray fouls the side of the cistern and wont allow it to float free and turn off the water. I only discovered this from bitter experience.
budgie, August 2008